This invention relates to an oral respiratory mask to provide breath-by-breath measurements of respiration and metabolism in adults or children. In particular, the invention relates to such a mask having minimum dead space, so as to improve the analytic quality of such measurements.
Breath-by-breath measurements of respiration and metabolism are useful in determining the over-all health or fitness of an individual and also in the identification of specific illnesses, especially illnesses related to the pulmonary and cardiovascular systems.
Typical measurements include measurements of such parameters as breath-by-breath volume, temperature, and exhaled gas composition. The volume of air measured is the volume which enters and leaves the lungs with each breath, which volume is referred to as tidal volume. Composition measurements typically include measurements such as percentage of carbon dioxide or moisture. Temperature measurements may include measurements of the temperature of air inhaled or exhaled with each breath.
Relatively high accuracy in the measurements of such parameters is required if the measurement is to be useful as an indicator of health or illness. If a parameter cannot be detected with relative accuracy and, thus, with certainty, an individual's health may not be properly assessed or an illness may go undetected. Thus, it is preferable for a mask used to make respiratory measurements to provide measurements of respiratory parameters that are as accurate as possible. Further, modern technology in analysis of exhaled gases has exceeded the ability of conventional mouth covering masks to provide satisfactory samples to the analysis equipment.
Conventional face masks used to measure respiratory parameters on a breath-by-breath basis inherently produce inaccurate measurements because the face masks have excessive dead space within the mask. Dead space is that space or cavity volume formed between the skin surface of the user within the mask and the internal surface or walls of the mask. While a small volume of dead air space will not normally cause appreciable inaccuracy in measurement, the dead space in conventional mouth covering masks is excessive and results in carbon dioxide rebreathing and other alterations in ventilatory response that provide somewhat inaccurate measurements. Further, where parameters are changing quickly, dead space may result in gasses from previous breaths being analyzed, as if such gasses were currently being exhaled, which can result in relevant analytical errors. Because compensation for the effects on measurements caused by rebreathing or ventilatory response alternations cannot usually be made, excessive dead air space results in a failure to accurately assess an individual's state of health.
Conventional face masks having excessive dead space typically have been of a design which enclosed a user's nose and mouth. Attempts have been made to lessen dead space associated with the mask by providing a breathing device for enclosing only the mouth, thus eliminating the dead space otherwise present in the proximity of the nose. However, such prior devices for only the mouth did not provide an adequate face seal and, thus, were eventually designed to be inserted in the user's mouth, held in position by the user's teeth with the user's lips acting as a seal. Even the mouth-held versions were often ineffective or completely unusable because the user's jaw and facial muscles would soon tire, reducing the effectiveness of the device. Such mouth-held devices were basically unusable by the infirm, who often require testing of this type, and by children.
The present invention overcomes the problems associated with excessive dead air space by providing a respiratory mask of a design minimizing the dead air space, yet effectively sealing with the face of the user. Moreover, the present invention provides a mask which, because of its curvature and flexibility, may be used to provide highly accurate breath-by-breath measurements of respiration and metabolism in adults and children.